- Methicillin-resistant Staphylococcus aureus (MRSA) is a highly problematic bacterial pathogen that has become a symbol of the global antibiotic resistance crisis. S. aureus is a Gram-positive bacterium that commonly lives on the skin and in the nasal passages of healthy individuals.
- While it is often harmless as part of the normal human microbiota, it can cause a wide range of infections, from minor skin and soft tissue infections to life-threatening conditions such as pneumonia, bloodstream infections, sepsis, and endocarditis. MRSA refers specifically to strains of S. aureus that have developed resistance to methicillin and other β-lactam antibiotics, including penicillins and cephalosporins, making them more difficult to treat.
- The resistance of MRSA to methicillin and related drugs is primarily due to the acquisition of the mecA gene, carried on a mobile genetic element known as the staphylococcal cassette chromosome mec (SCCmec). This gene encodes an altered penicillin-binding protein (PBP2a), which has a low affinity for β-lactam antibiotics. Normally, β-lactams kill bacteria by inhibiting PBPs, which are enzymes essential for bacterial cell wall synthesis. However, in MRSA, PBP2a allows cell wall production to continue even in the presence of antibiotics, conferring high-level resistance. In addition, MRSA strains often carry other resistance genes, making them resistant to multiple drug classes and further complicating treatment.
- Clinically, MRSA infections are divided into two main categories: healthcare-associated MRSA (HA-MRSA) and community-associated MRSA (CA-MRSA). HA-MRSA typically occurs in hospitalized or immunocompromised patients, often involving invasive infections such as bloodstream infections, surgical site infections, and pneumonia. These infections are frequently linked to the use of catheters, ventilators, or surgical procedures. In contrast, CA-MRSA infections emerge in otherwise healthy individuals outside healthcare settings, commonly presenting as skin and soft tissue infections such as boils, abscesses, and cellulitis. CA-MRSA strains often spread through close physical contact and are a concern in settings like schools, gyms, and military barracks.
- The spread of MRSA poses major challenges for healthcare systems worldwide. Infections caused by MRSA are associated with higher morbidity, longer hospital stays, increased medical costs, and greater mortality compared to infections with methicillin-sensitive S. aureus (MSSA). Standard treatments such as methicillin, oxacillin, or cephalosporins are ineffective against MRSA, necessitating the use of alternative antibiotics such as vancomycin, linezolid, daptomycin, or newer agents like ceftaroline. However, resistance to some of these drugs has also emerged, raising concerns about the potential for “untreatable” S. aureus infections in the future.
- Public health efforts to combat MRSA focus on infection prevention and control, particularly in hospitals. Strategies include rigorous hand hygiene, screening and isolating colonized patients, decontaminating hospital environments, and prudent use of antibiotics to reduce selective pressure. In community settings, education about personal hygiene, wound care, and the dangers of sharing personal items has been important in curbing transmission. Additionally, research is exploring novel strategies such as vaccines, bacteriophage therapy, and antimicrobial peptides to manage MRSA infections.
